The Controller tool lets you generate MIDI controller messages, such as volume and pan. There are sixteen sliders, each corresponding to one of the sixteen MIDI channels. Moving a slider will generate messages on that channel. The menu button in the upper-left corner lets you specify which type of message is generated. Some of the message types (for example, "reverb depth") are specific to General MIDI devices.

The Send button, when pressed, will send the current controller values (as specified by the current settings of the 16 sliders) to MIDI output. The Snarf button will take all of these messages and, rather than sending them to MIDI output, put them in the Snarf buffer.